X-ray Computed Tomography (CT) is a technique that produces a cross-sectional image of an object from a series of attenuation measurements taken from different angles around the object. CT reconstructed data can provide precise, quantitative information about the characteristics of objects in the scan plane, for instance physical density. While CT technology has been largely applied in medical fields, problems associated with the technology have limited its applicability to other fields. A primary problem with most CT methods is that they are time consuming. Consequently, prior to this invention, CT technology has not been a feasible alternative to such problems as screening luggage for concealed items.
Screening luggage for concealed items is of vital importance. Such monitoring is necessary to avoid smuggling of drugs and to detect explosives planted in luggage by terrorists. Present techniques for screening luggage include manual inspection. Manual inspection is a time consuming and therefore expensive operation. Moreover, manual inspection is not particularly effective unless suspicious items such as transistor radios are routinely disassembled and checked for hidden items.
Thermal Neutron Activation (TNA) systems have been employed in the prior art to detect explosives in luggage. This technique relies upon the detection of the nitrogen associated with explosives. While the technique has enjoyed some success, there are a number of problems associated with it. Namely, the technique is slow because many innocuous items cause false alarms which must be resolved with additional measures.
Another common baggage inspection device is the X-ray line scanner ("concourse scanner") used in practically all public airports. Such systems are deficient in several respects. First, they are merely imaging devices without the capability of automatically identifying target materials like explosives. They also form a cluttered image in which items in a container are projected together and overlaid on each other. These systems require an operator to study and interpret the projection images. Operator fatigue and distraction augment the imperfect nature of the projection method itself.